Early-Universe-Physics Insensitive and Uncalibrated Cosmic Standards: Constraints on $Ω_{\rm{m}}$ and Implications for the Hubble Tension

Abstract

To further shed light on whether pre-recombination models can resolve the Hubble tension, we explore constraints on the cosmic background evolution that are insensitive to early-universe physics. The analysis of the cosmic microwave background (CMB) anisotropy has been thought to highly rely on early-universe physics. However, we show that the difference between the sound horizon at recombination and that at the end of the drag epoch is small and insensitive to early-universe physics. This allows us to link the absolute sizes of the two horizons and treat them as free parameters. Jointly, the CMB peak angular size, Baryon Acoustic Oscillations (BAO), and Type Ia supernovae can be used as "early-universe-physics independent and uncalibrated cosmic standards", which measure the cosmic history from recombination to today. They can set strong and robust constraints on the post-recombination cosmic background, especially the matter density parameter with Ωm = 0.302 ± 0.008 (68% C.L.). When combined with other non-local observations that are independent of or insensitive to early-universe physics, we obtain several constraints on H0 that are currently more consistent with the Planck 2018 result than the local measurement results such as those based on Cepheids. These results suggest a tension between the post-recombination, but non-local, observations and the local measurements. This tension cannot be resolved by modifying the pre-recombination early universe physics.

Hints of FLRW Breakdown from Supernovae

“…This is currently the front-running idea. However, it has become apparent that early Universe resolutions to Hubble tension typically exacerbate other discrepancies [13][14][15][16][17][18][19][20]. Moreover, it should be stressed that the introduction of new early Universe physics has only one real motivation, essentially to bring the Baryon Acoustic Oscillation (BAO) scale into line with Cepheidcalibrated SN.…”

“…[52] We stress that this maximum H 0 can only be achieved if one allows an alteration of the sound horizon with new early Universe physics. Evidently, local determinations of H 0 ∼ 73 km/s/Mpc can be tolerated within 2σ, provided one ignores the tendency of new early Universe physics [9][10][11][12] to exacerbate σ 8 tension [13][14][15][16][17][18][19][20]. Trouble is clearly brewing.…”

Is Local $H_0$ At Odds With Dark Energy EFT?

“…Based on these results, it is reasonable to expect that the S 8 considerations should only strengthen our results here that the DE EFT framework is less likely to hold the answer to the cosmic tensions, but one is always free to venture theoretically beyond EFT, e. g. [130,131]. In the big picture, if attempts to alter the BAO scale through EDE or equivalent are discredited [80][81][82][83][84][85][86][87][88][89], one is confronted with a Λ that does not appear to admit an EFT description. If confirmed, this in itself is an extremely profound insight into the cosmological constant Λ.…”

“…as viable DE models. That being said, the age of both the universe and astrophysical objects within it bound H 0 73 at 2σ confidence interval within FLRW cosmology [75,79], so even if EDE works which at present this is far from clear [80][81][82][83][84][85][86][87][88][89], it is plausible that local H 0 may still be biased high. 7 Note added: While we were in the final stages of preparation for the arXiv submission, two papers [60,61] appeared that have good overlap, and of course are compatible with our main results and statements.…”

Consistency of Planck, ACT and SPT constraints on magnetically assisted recombination and forecasts for future experiments

“…Combining Planck with either BAO+SN, ACT or SPT results in a marginal shift of the peaks of the posteriors toward a non-zero b. In the case of the BAO+SN, it is due to the mild preference of the BAO data, when analyzed in a recombination-model-independent way [110,111], for a smaller value of the sound horizon at decoupling, r drag , and, hence, a larger H 0 , and the fact that clumping reduces r drag .…”